Studies of the morphological effects of antimalarial drugs on malarial parasites yield important information on the site of action of the drugs. Changes in the structure of the malarial parasites furnish clues to the mode of drug action. We have demonstrated during the past five years that such studies are particularly revealing when made with electron microscopy and autoradiography. In the research proposed I shall attempt to study by electron microscopy the action of antimalarial drugs on the erythrocytic and exoerythrocytic stages of primate malarial parasites, since data obtained from studies of primate malarial parasites will be more applicable to the human malarial parasites o than would studies of avian and rodent malarias. Antimalarial drugs to be used will include antibiotics such as lincomycin, and its analogues, tetracycline and doxycycline, all of which have been shown to be antimalarials in recent years. Since lincomycin has been demonstrated to affect ribosomes, isolation of ribosomes of malarial parasites before and after treatment will be performed and the structure of the ribosomes will be analysed. Also, I plan to apply autoradiographic techniques to trace the pathway of the antimalarial drugs by electron microscopy. Experiments with 8- aminoquinollines and 4-aminoquinolines will continue. These studies will shed light on the specific sites of activity of these drugs. A better understanding of the mode of action of these drugs will contribute to a better understanding of malaria treatment.